riscv: Add jump-label implementation

Add jump-label implementation based on the ARM64 version
and add CONFIG_JUMP_LABEL=y to the defconfigs.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Reviewed-by: Björn Töpel <bjorn.topel@gmail.com>
Tested-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Documentation/features/core/jump-labels/arch-support.txt

@@ -23,7 +23,7 @@
     |    openrisc: | TODO |
     |      parisc: |  ok  |
     |     powerpc: |  ok  |
-    |       riscv: | TODO |
+    |       riscv: |  ok  |
     |        s390: |  ok  |
     |          sh: | TODO |
     |       sparc: |  ok  |

arch/riscv/Kconfig

@@ -47,6 +47,8 @@ config RISCV
 	select GENERIC_TIME_VSYSCALL if MMU && 64BIT
 	select HANDLE_DOMAIN_IRQ
 	select HAVE_ARCH_AUDITSYSCALL
+	select HAVE_ARCH_JUMP_LABEL
+	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN if MMU && 64BIT
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_KGDB_QXFER_PKT

arch/riscv/configs/defconfig

@@ -17,6 +17,7 @@ CONFIG_BPF_SYSCALL=y
 CONFIG_SOC_SIFIVE=y
 CONFIG_SOC_VIRT=y
 CONFIG_SMP=y
+CONFIG_JUMP_LABEL=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 CONFIG_NET=y

arch/riscv/configs/nommu_k210_defconfig

@@ -33,6 +33,7 @@ CONFIG_SMP=y
 CONFIG_NR_CPUS=2
 CONFIG_CMDLINE="earlycon console=ttySIF0"
 CONFIG_CMDLINE_FORCE=y
+CONFIG_JUMP_LABEL=y
 # CONFIG_BLOCK is not set
 CONFIG_BINFMT_FLAT=y
 # CONFIG_COREDUMP is not set

arch/riscv/configs/nommu_virt_defconfig

@@ -30,6 +30,7 @@ CONFIG_MAXPHYSMEM_2GB=y
 CONFIG_SMP=y
 CONFIG_CMDLINE="root=/dev/vda rw earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0"
 CONFIG_CMDLINE_FORCE=y
+CONFIG_JUMP_LABEL=y
 # CONFIG_BLK_DEV_BSG is not set
 CONFIG_PARTITION_ADVANCED=y
 # CONFIG_MSDOS_PARTITION is not set

arch/riscv/configs/rv32_defconfig

@@ -17,6 +17,7 @@ CONFIG_BPF_SYSCALL=y
 CONFIG_SOC_VIRT=y
 CONFIG_ARCH_RV32I=y
 CONFIG_SMP=y
+CONFIG_JUMP_LABEL=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 CONFIG_NET=y

arch/riscv/include/asm/jump_label.h

@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Emil Renner Berthing
+ *
+ * Based on arch/arm64/include/asm/jump_label.h
+ */
+#ifndef __ASM_JUMP_LABEL_H
+#define __ASM_JUMP_LABEL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+#include <asm/asm.h>
+
+#define JUMP_LABEL_NOP_SIZE 4
+
+static __always_inline bool arch_static_branch(struct static_key *key,
+					       bool branch)
+{
+	asm_volatile_goto(
+		"	.option push				\n\t"
+		"	.option norelax				\n\t"
+		"	.option norvc				\n\t"
+		"1:	nop					\n\t"
+		"	.option pop				\n\t"
+		"	.pushsection	__jump_table, \"aw\"	\n\t"
+		"	.align		" RISCV_LGPTR "		\n\t"
+		"	.long		1b - ., %l[label] - .	\n\t"
+		"	" RISCV_PTR "	%0 - .			\n\t"
+		"	.popsection				\n\t"
+		:  :  "i"(&((char *)key)[branch]) :  : label);
+
+	return false;
+label:
+	return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key,
+						    bool branch)
+{
+	asm_volatile_goto(
+		"	.option push				\n\t"
+		"	.option norelax				\n\t"
+		"	.option norvc				\n\t"
+		"1:	jal		zero, %l[label]		\n\t"
+		"	.option pop				\n\t"
+		"	.pushsection	__jump_table, \"aw\"	\n\t"
+		"	.align		" RISCV_LGPTR "		\n\t"
+		"	.long		1b - ., %l[label] - .	\n\t"
+		"	" RISCV_PTR "	%0 - .			\n\t"
+		"	.popsection				\n\t"
+		:  :  "i"(&((char *)key)[branch]) :  : label);
+
+	return false;
+label:
+	return true;
+}
+
+#endif  /* __ASSEMBLY__ */
+#endif	/* __ASM_JUMP_LABEL_H */

arch/riscv/kernel/Makefile

@@ -53,4 +53,6 @@ endif
 obj-$(CONFIG_HOTPLUG_CPU)	+= cpu-hotplug.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
 
+obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
+
 clean:

arch/riscv/kernel/jump_label.c

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Emil Renner Berthing
+ *
+ * Based on arch/arm64/kernel/jump_label.c
+ */
+#include <linux/jump_label.h>
+#include <linux/kernel.h>
+#include <linux/memory.h>
+#include <linux/mutex.h>
+#include <asm/bug.h>
+#include <asm/patch.h>
+
+#define RISCV_INSN_NOP 0x00000013U
+#define RISCV_INSN_JAL 0x0000006fU
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	void *addr = (void *)jump_entry_code(entry);
+	u32 insn;
+
+	if (type == JUMP_LABEL_JMP) {
+		long offset = jump_entry_target(entry) - jump_entry_code(entry);
+
+		if (WARN_ON(offset & 1 || offset < -524288 || offset >= 524288))
+			return;
+
+		insn = RISCV_INSN_JAL |
+			(((u32)offset & GENMASK(19, 12)) << (12 - 12)) |
+			(((u32)offset & GENMASK(11, 11)) << (20 - 11)) |
+			(((u32)offset & GENMASK(10,  1)) << (21 -  1)) |
+			(((u32)offset & GENMASK(20, 20)) << (31 - 20));
+	} else {
+		insn = RISCV_INSN_NOP;
+	}
+
+	mutex_lock(&text_mutex);
+	patch_text_nosync(addr, &insn, sizeof(insn));
+	mutex_unlock(&text_mutex);
+}
+
+void arch_jump_label_transform_static(struct jump_entry *entry,
+				      enum jump_label_type type)
+{
+	/*
+	 * We use the same instructions in the arch_static_branch and
+	 * arch_static_branch_jump inline functions, so there's no
+	 * need to patch them up here.
+	 * The core will call arch_jump_label_transform  when those
+	 * instructions need to be replaced.
+	 */
+}